Discovered this earlier in the week. It's fun, and possibly even
educational.
Basically, draw shapes, attach them together with motors and springs,
and then let physics do its stuff.
http://www.phun.at/
Not opensource (unfortunately), but downloads are available for Linux
x86 and AMD64 (and yes, it requires some graphics, possibly even
opengl, though it is 2D).
-- 
Be seeing you,                         http://www.glendale.org.uk
Sam.                        Mail/IM (Jabber): sam@???